C241 Lanczos Time – 515 Hours

My C241 number from Makoto’s list* has finally started the Lanczos step. But at 515 hours, I won’t even get the answer this year. 🙂 I did think it would probably be a long calculation after getting past 100 million relations and producing a 13.2M x 13.2M matrix !

Now all we can do is wait. At least the Msieve program provides a checkpoint every 12 (?) hours so we can breathe easy. The Lanczos algorithm is equivalent to inverting a matrix – in this case solving a system of 13.2 million linear equations with 13.2 million variables. Gasp !

To see the full width of the above picture, it is best viewed with a horizontal screen resolution of 1,280 or more. However, if viewing at a lower resolution and you are using Opera, just hit the “-” key a couple of times to shrink the image slightly. “*” will bring you instantly back to your normal resolution.

* This composite number is from the partial factorisation of the 242-digit number 177777… (7 repeated 241 times), or:

(16·10241-7)/9 = 17241 = 17 · C241

See the factorisation website of Makoto Kamada for other incredible results.